"Just heard 2 in marin recently went to mexico," he posted on Twitter, the social networking and miniblogging site, in reference to news about apparent infections in Marin County. And after he declared a state of emergency over the outbreak, the governor tweeted: "There is no need for alarm."

Swine flu remained the No. 1 topic Wednesday on Twitter, the popular site that allows users to post real-time updates of 140 characters or less. The nonstop stream of comments on the service in the past week have been both accurate and grossly misinformed, leading some critics to question whether such fast-flowing – and increasingly popular – new media tools are helping spread valuable information about the outbreak or simply fanning panic.

"The use of Twitter as a forum to discuss a frightening illness has less to do with updating people with news stories and other developments – it's about spreading gossip, panicking, and potentially misinforming one's followers about a grave concern," wrote Brennon Slattery on his blog at PCWorld.com.

The CDC is constantly monitoring Twitter and other social media sites, says spokeswoman Shelly Diaz, and it will move to correct misinformation when necessary. "We realize that the landscape of media has changed a lot, and we want to make sure we are reaching everyone."

You have to consider the net effect of Twitter on the national conversation on swine flu, points out Clay Shirky, adjunct professor at New York University's graduate Interactive Telecommunications Program. It's unfair to view one or two posts in a vacuum, he says, instead of looking at the arc of the discussion on Twitter and other social networking sites.

"Twitter has done a pretty good job," he says, not only in getting out basic information about what's happening with the outbreak, but also in generating "countervailing points of view" that might mitigate some of the panic.

But, he acknowledges, "Emotion moves faster than thought." And that can often lead to absurd tweets, or posts.

One Twitter user posted, "How long before the Swine Flu hysteria crashes the pork market?"

But, in an example of how interactive online media can also self-correct quickly, another Twitterer soon piped up to counter: "People! Swine flu has nothing to do with eating pork!"

The CDC has also stepped in to correct the record. After some users speculated about the possible danger in eating pork, it had this tweet: "CDC reminds you that you can NOT get swine flu from eating pork."

CDC twitters

The CDC has had its own Twitter account since January, when it was using it to update users on an outbreak of salmonella. Since then it has used Twitter to provide basic information about everything from seasonal illnesses to how to say warm during the winter.

Even though it's relatively new to Twitter, the CDC has been pushing into social networking sites over the past few years with a presence on MySpace and Facebook, among other online forums.

"CDC has to be where people are. And people are increasingly in the social media forums," said Janice Nall, director of eHealth Marketing for the CDC, at a healthcare marketing event last year. "And if they are talking about HIV and how to prevent it on MySpace, we need to be there with credible, accurate information."

But now that the CDC has established itself in the Web 2.0 world of social networks, Mr. Morozov wrote on his blog, it should do more to make itself heard above the online chatter.

"In an ideal world, they would have established ownership of most online conversations from the very beginning, posting updates as often as they can. Instead, they are now faced with the prospect of thousands of really fearful citizens, all armed with their own mini-platforms to broadcast their fears – which may cost it dearly in the long term," he wrote.

The CDC and other government agencies face a dilemma when it comes to interacting with the fast pace of online conversation, says Mr. Shirky. "There are a bunch of pressures not to overreact to these things. But change in the communication infrastructure means that the CDC has to be clearer with the public than it has before."

More people seek information online

More than ever, the public is going online to find the latest information about public-health concerns – and find new tools to track the swine flu outbreak.

Nielsen reported Tuesday that 4 percent of the blogs and news discussion forums that it regularly tracks were related to swine flu. Conversations about the outbreak were 10 times more than that of the salmonella scare earlier this year.

One health researcher is even tracking reported cases of flu with an interactive Google map. And the user-generated online encyclopedia, Wikipedia, has an expanding page dedicated to the outbreak.

How all of this fast-moving and free-flowing information will eventually impact a public-health emergency is still unclear. But there has been at least one example where putting a mass communication tool in the hands of the masses made a big positive difference.

After the Sichuan earthquake last year in China, says Shirky, Twitter was one way to receive and spread news about the quake's impact – and to get out information about where donations were needed most desperately.